Measuring complex PCB-based interconnects in a production environment

Abstract

A measuring system and method is configured to analyze numerous different types of interconnects having varying degrees of complexity. The measuring system and method characterizes an interconnect to be tested by a predefined reflection coefficient signature. Each specific interconnect is predefined by a reflection coefficient signature that is unique to that specific interconnect. Once the reflection coefficient signature is defined, a corresponding reflection envelope is defined which defines boundary limits about the reflection coefficient signature. Subsequent testing of the specific interconnect results in a measured reflection coefficient curve, which is compared to the corresponding reflection envelope. The specific interconnect under test is considered acceptable if the values of the measured reflection coefficient curve do not fall outside the reflection envelope. If one or more values of the measured reflection coefficient curve fall outside the reflection envelope, then the specific interconnect under test fails the test.

What is claimed is: 
     
       1. A method of testing a printed circuit board, the method comprising:
 a. defining a specific interconnect structure of the printed circuit board to be tested; 
 b. defining a predetermined reflection coefficient signature corresponding to the specific interconnect structure; 
 c. defining a reflection envelope around the reflection coefficient signature, wherein the reflection envelope defines tolerance boundaries on both sides of the reflection coefficient signature; 
 d. measuring a reflection coefficient for the specific interconnect structure to determine a measured reflection coefficient curve corresponding to the specific interconnect structure; and 
 e. comparing the measured reflection coefficient curve to the reflection envelope, wherein if all values of the measured reflection coefficient curve are within the reflection envelope then the specific interconnect structure passes the test, and if one or more values of the measured reflection coefficient curve are not within the reflection envelope then the specific interconnect structure fails the test. 
 
     
     
       2. The method of  claim 1  wherein the reflection coefficient signature includes a curve, each point on the curve defining a reflection coefficient value versus time. 
     
     
       3. The method of  claim 2  wherein one or more portions of the reflection coefficient signature are a non-linear curve. 
     
     
       4. The method of  claim 1  wherein defining the reflection coefficient signature comprises performing a computer simulation using a computer design of the printed circuit board and calculating a simulated reflection coefficient curve according to the simulation, wherein the simulated reflection coefficient curve is the reflection coefficient signature. 
     
     
       5. The method of  claim 1  wherein defining the reflection coefficient signature comprises manufacturing a prototype interconnect structure and measuring the reflection coefficient curve of the prototype interconnect structure. 
     
     
       6. The method of  claim 1  wherein measuring the reflection coefficient is performed using time domain reflectometry. 
     
     
       7. The method of  claim 1  wherein each specific interconnect structure has a unique reflection coefficient signature. 
     
     
       8. The method of  claim 1  wherein different portions of the reflection envelope have different tolerances relative to a corresponding portion of the reflection coefficient signature. 
     
     
       9. The method of  claim 1  wherein the reflection envelope is fine-tuned to match a corresponding shape of the reflection coefficient signature. 
     
     
       10. The method of  claim 1  wherein the reflection envelope includes an upper limit boundary and a lower limit boundary around the reflection coefficient signature. 
     
     
       11. The method of  claim 1  wherein the reflection coefficient signature is time-based and the measured reflection coefficient curve is time-based. 
     
     
       12. A testing device comprising:
 a. a measurement module configured to measure a reflection coefficient for a specific interconnect structure to determine a measured reflection coefficient curve corresponding to the specific interconnect structure; 
 b. a memory configured to store a reflection envelope, wherein the reflection envelop defines tolerance boundaries around a reflection coefficient signature corresponding to the specific interconnect structure; and 
 b. a processor configured to compare the measured reflection coefficient curve to the reflection envelope, wherein if all values of the measured reflection coefficient curve are within the reflection envelope then the specific interconnect structure passes the test, and if one or more values of the measured reflection coefficient curve are not within the reflection envelope then the specific interconnect structure fails the test. 
 
     
     
       13. The testing device of  claim 12  wherein the reflection coefficient signature includes a curve, each point on the curve defining a reflection coefficient value versus time. 
     
     
       14. The testing device of  claim 13  wherein one or more portions of the reflection coefficient signature are a non-linear curve. 
     
     
       15. The testing device of  claim 12  wherein the measurement module is configured to measure the reflection coefficient using time domain reflectometry. 
     
     
       16. The testing device of  claim 12  wherein each specific interconnect structure has a unique reflection coefficient signature. 
     
     
       17. The testing device of  claim 12  wherein different portions of the reflection envelope have different tolerances relative to a corresponding portion of the reflection coefficient signature. 
     
     
       18. The testing device of  claim 12  wherein the reflection envelope is fine-tuned to match a corresponding shape of the reflection coefficient signature. 
     
     
       19. The testing device of  claim 12  wherein the reflection envelope includes an upper limit boundary and a lower limit boundary around the reflection coefficient signature. 
     
     
       20. The testing device of  claim 12  wherein the reflection coefficient signature is time-based and the measured reflection coefficient curve is time-based.